关于计算器的问题

[code=VB][/code]
Dim num1, t, d, cat, a
Private Sub Command1_Click(Index As Integer)
If Index <= 9 Then
  If t > 9 And t <> 15 Then
  Text1.Text = Index
  Else
  If Text1.Text = "0" Then
  Text1.Text = Index
  Else
  Text1.Text = Text1.Text & Index
  End If
  End If
Else
  Select Case Index
  Case 10 '加法
  If cat = 2 Then
  num1 = num1 - Val(Text1.Text)
  Text1.Text = num1
  ElseIf cat = 3 Then
  num1 = num1 * Val(Text1.Text)
  Text1.Text = num1
  ElseIf cat = 4 Then
  num1 = num1 / Val(Text1.Text)
  Text1.Text = num1
  ElseIf d = 0 Then
  d = 1
  num1 = Text1.Text
  Text1.Text = 0
  Else
  num1 = num1 + Val(Text1.Text)
  Text1.Text = num1
  End If
  cat = 1
  p = 0
  Case 11 '减法
  If cat = 1 Then
  num1 = num1 + Val(Text1.Text)
  Text1.Text = num1
   
  ElseIf cat = 3 Then
  num1 = num1 * Val(Text1.Text)
  Text1.Text = num1
   
  ElseIf cat = 4 Then
  num1 = num1 / Val(Text1.Text)
  Text1.Text = num1
  ElseIf d = 0 Then
  d = 1
  num1 = Text1.Text
  Text1.Text = 0
  Else
  num1 = num1 - Val(Text1.Text)
  Text1.Text = num1
  End If
  cat = 2
  p = 0
  Case 12 '乘法
  If cat = 1 Then
  num1 = num1 + Val(Text1.Text)
  Text1.Text = num1
   
  ElseIf cat = 2 Then
  num1 = num1 - Val(Text1.Text)
  Text1.Text = num1
   
  ElseIf cat = 4 Then
  num1 = num1 / Val(Text1.Text)
  Text1.Text = num1
  ElseIf d = 0 Then
  d = 1
  num1 = Text1.Text
  Text1.Text = 0
  Else
  num1 = num1 * Val(Text1.Text)
  Text1.Text = num1
  End If
  cat = 3
  p = 0
  Case 13 '除法
  If cat = 1 Then
  num1 = num1 + Val(Text1.Text)
  Text1.Text = num1
  ElseIf cat = 2 Then
  num1 = num1 - Val(Text1.Text)
  Text1.Text = num1
  ElseIf cat = 3 Then
  num1 = num1 * Val(Text1.Text)
  Text1.Text = num1
  ElseIf d = 0 Then
  d = 1
  num1 = Text1.Text
  Text1.Text = 0
  Else
  num1 = num1 / Val(Text1.Text)
  Text1.Text = num1
  End If
  cat = 4
  p = 0
  Case 15 '小数点
  If p = 0 Then
  Text1.Text = Text1.Text + "."
  p = 1
  End If
  
  
  
  Case 16 '等于
   
  If cat = 1 Then
  num1 = num1 + Val(Text1.Text)
  Text1.Text = num1
  ElseIf cat = 3 Then
  num1 = num1 + Val(Text1.Text)
  Text1.Text = num1
   
  ElseIf cat = 2 Then
  num1 = num1 - Val(Text1.Text)
  Text1.Text = num1
   
  ElseIf cat = 4 Then
  num1 = num1 / Val(Text1.Text)
  Text1.Text = num1
  End If
  p = 0
  End Select
End If
t = Index
End Sub

Private Sub Command2_Click()
a = Len(Text1.Text)
If a = 1 Then
Text1.Text = 0
Else
Text1.Text = Left(Text1.Text, a - 1)
End If

End Sub

Private Sub Command3_Click()
Text1.Text = 0
num1 = 0
d = 0
p = 0
End Sub

Private Sub Form_Load()
d = 0
End Sub

我想在点击一次小数点以后 删除小数点 能继续点出小数点 而只能有1个 。 跪求指导哇